The invention relates to a device for welding overlapping foil edges with a heater, with contact rollers for the exterior contact at the foil edges as well as at least one height adjustment device, whereby the height adjustment device has a guide device for movement control of the respective contact roller essentially transversely to the processing direction of the foil edges, as well as a drive for moving this contact roller.
Devices for the overlapping welding of foil edges are described in DE-OS 35 35 759, DE-OS 40 00 017, and DE-GM 88 16 287.7. The devices are used particularly for welding foils in waste dump construction. Hereby high requirements are posed on the quality of the welding.
During the welding of the foil edges, the device drives along the two edges of the foils, whereby the foil edges are arranged so as to be overlapping. In the process, the foil edges enter the device on top of each other and are then guided over a heater which as a rule is constructed in a wedge-shape. This wedge-shaped heater is arranged lying down, i.e. the two partial surfaces which converge backwards toward the wedge tip are positioned on top of each other. Hereby the heater is oriented with its obtuse end toward the entrance of the foil edges into the device.
Each wedge surface of the heater may be divided into two partial wedge surfaces which are arranged at a distance from each other and between which a groove extends. The top foil edge is hereby passed over the two top partial wedge surfaces and the bottom foil edge is passed over the two bottom partial wedge surfaces. Both of the respective superposed partial wedge surfaces combine toward the back, forming a line-shaped wedge tip where the two foil edges are brought together.
The heater has several heating elements which ensure heating of the wedge surfaces which function as heating surfaces. Hereby the heating plasticizes the foil edges in the area of the partial wedge surfaces in such a way that they are welded together after being brought together, resulting, in particular due to the partial wedge surfaces which are arranged at a distance from each other, in two weld seams which extend parallel to each other at a corresponding distance. Between the weld seams a channel is formed which, in order to test the tightness of the weld seams, is closed off at one end, whereupon air is introduced into its other end. If there is no leaking of air during this test, the weld seams are correct.
In order that the foil edges are guided past the heating surfaces of the heater with contact, and in particular are then passed together with the pressure required for welding, contact rollers have been provided in the heater area itself and behind the heater, i.e. one contact roller for each of the two parallel weld seams. If the contact rollers are located behind the heater, two contact rollers are arranged on top of each other in order to be able to exert pressure from both sides on the corresponding heated areas of the foil edges. One pair each of the contact rollers behind the heater simultaneously function as drive rollers, i.e. at least one of the rollers is equipped with a drive which pulls the foil edges into the device and hereby drives the device forward.
In the devices according to DE-OS 35 35 759 and German OS 40 00 017 contact rollers are suspended on plate springs which press them with a preload against the heater or against a stationary contact roller facing it. There is no height adjustment device to adapt the device to different thicknesses of the foil edges. But a height adjustment device is found in the device according to DE-GM 88 16 287.7. It consists of a pneumatic cylinder whose piston rod acts directly on one of two opposing contact rollers. Hereby the contact roller movement is essentially guided transversely to the processing direction of the foil edges by the pneumatic cylinder, i.e. via the guiding of its piston and piston rod.
Such a height adjustment device on the one hand presupposes the existence of a source of compressed air. This significantly restricts the application of the device. Especially in the waste dump field where the device is used primarily, compressed air sources are frequently not available. Another disadvantage is that no gap between the two contact rollers or between one contact roller and the heater can be set, which makes it difficult to generate reproducible pressure conditions. However, the quality of the weld seams when connecting two foil edges also depends essentially on the contact pressure generated by the contact rollers. Finally, with the pressures occurring here, the pneumatic cylinders have a tendency to jam the piston rod in the cylinder.